I've watched a fair number of weed smoker's lives (~10) and they fall into two distinct categories.

One set smoke weed and then partake in creative, explorative, or otherwise effort filled pursuits. Generally I feel that weed has likely improved their lives.

The other set smoke weed and consume... consume tv, consume video games, consume food, consume music. These people seem to fall into a slump that weed seems to participate in keeping them in. Weed lowers the bar to enjoy yourself and thus raises the bar for other activities. If weed and video games feels good, then why call up friends and go bowling? It's not addictive, but it does have a kind of gravity because it's an activity that participates in the economy of potential activities. For these people weed entertains them, at the cost of them becoming a more boring person.